Charged Particle Self-Scattering and Acceleration in Reconnection

Unlike X-point small-scale reconnection, which develops strong electric fields and accelerates particles naturally, large-scale reconnection cannot rely on electric fields; rather it has to rely on more classic stochastic mechanisms. Only these stochastic mechanisms allow acceleration up to the Hillas limit, this is usually assumed, but rarely well argued. One of the stochastic mechanisms has to do with straightening magnetic field lines that provide curvature acceleration. The other, having to do with compression in the inflow, is similar to the shock acceleration. All stochastic mechanisms have to do with efficient particle scattering, yet the mechanism for scattering remains elusive. In this presentation I show the results of simulations where particles stream along field lines and scatter by self-generated turbulence. Surprisingly, their dynamics is not diffusive but rather superdiffusive. This superdiffusion depends on particle energy. I will discuss implications of this to the standard stochastic acceleration picture applied to reconnecting current layers.